Method for forming an initial profile or a tool of the kind and a profile therefor

ABSTRACT

A process for forming a starting profile with a profile cavity by a bending forming process and an internal high pressure produced in a sealed profiled cavity by way of a fluid, including the steps of initially, before forming by internal high pressure, forming a starting profile at a distance from free ends of the starting profile and across a longitudinal axis of the starting profile into a cross-section with favorable bending properties, by one of transversely inwardly bent side walls of the starting profile, folding during bending, flat pressing or a flat high-sided profile produced in an extrusion process.

PRIORITY CLAIM

This is a U.S. national stage of application No. PCT/CH00/00594, File onNov. 8, 2000. Priority is claimed on that application and on thefollowing application:

Country: Germany, Application No.: 19955694.6, Filed: Nov. 18, 1999.

BACKGROUND OF THE INVENTION

This invention relates to a process for forming a starting profile or asimilar workpiece into an end profile by means of an internal highpressure produced in the sealed profile cavity by way of a fluid activemeans, in particular for forming until the end profile rests against thewall of a form chamber. In addition, the invention comprises a profilewith a profile area separated by at least one profile wall as a startingprofile for the performance of the process.

In so-called internal high pressure forming (IHPF process) a hollowprofile is elongated by means of internal pressure. In addition, thehollow profile can be pushed by means of at least one pusher on theworkpiece and stretched, compressed, or expanded.

DE 35 32 499 C1 discloses for example a device to hydraulically expand apipe section by using a peg-like cylindrical probe inserted in the pipe,which by means of at least two spaced ring seals creates a seal areawith the pipe section to be expanded, which is filled with pressuremedium in order to expand the pipe. Before the start of the expandingprocess, the two ring seals are filled with pressure medium to seal thering gap between the probe and the pipe. The pressure medium is suppliedto the ring area by way of at least one reception slot and is controlledby a ring seal which serves as a valve and which closes the openingfound between the reception slot and the ring area until it has achievedits seal effect by way of elastic expansion.

This internal high pressure forming or hydro-forming is increasinglyused as an economic manufacturing procedure for bodywork components incar construction. Tubular steel is predominately used as the startingmaterial. Recently, for IHPF processes, aluminium material has also beenadded to the steel. In the same way as steel, this gives manufacturingprocedures in which tubes of sheet aluminium are used as startingmaterial; however, aluminium extrusion profiles may also be used as analternative. This is out of the question in the case of steel foreconomic reasons. The use of extrusion profiles has the decisiveadvantage that there are almost no limits to the shaping of the startingprofile.

For forming metallic tubes or extrusion profiles by means of bending, anattempt is generally made to organise the bending process in such a waythat the starting cross-section of the workpiece remains contained inthe then curved workpiece. Folds on the internal radius and on the outerradius should be avoided. Various techniques have been developed inorder to achieve this aim; as an example a few such procedures arelisted:

stretch bending;

bending over a mandrel;

hot bending.

Such bending techniques are also applied in the case of curvedhydro-forming components, the manufacture of which involves a bendingprocess before internal high pressure forming.

In view of these facts, the object of the present invention is to findan alternative bending procedure for hydro-forming components, therebydeliberately avoiding in the bending forming process the aim of givingor maintaining a shape which most closely resembles the contours of thefinal cross-section to be formed.

The doctrine of the independent claim leads to solution of this task;the sub-claims indicate favourable further embodiments. In addition theinvention includes all combinations of at least two of thecharacteristics contained in the description, the depiction and/or theclaims.

In accordance with this invention, before forming through internal highpressure, the starting profile at a distance from its free ends andacross its longitudinal axis is formed into a cross-section withfavourable bending properties, notably into a flat or roughly ovalcross-section. It has also proved favourable to assign to a tool thestarting profile with the area to be distorted, which for example isextruded from a light metal alloy or bent and constructed from a sheetmetal, and to distort the cross-section by means of this tool; inaddition the starting profile should be bent after the distortioncross-sectionally around this area.

The invention also includes mounting the starting profile on astationary tool and distorting and bending its cross-section by way of atranslatory and rotationally movable counter-tool.

An advantageous starting profile for the procedures in accordance withthis invention is an approximately H-shaped cross-section with tworoughly parallel chambers connected to each other. Their supportingwalls should be cross-sectionally bent inwards, whereas the innerboundaries of the chambers are formed by groove-like recesses.

In this case a combined bending IHPF process is used for which no limitsare set regarding the choice of starting material in principle; thelatter can for example be aluminium, steel or any other metal, ifnecessary even a non-metallic material. The following bending proceduremethods can be distinguished for use in combination with the IHPFprocess:

a preceding deformation into a cross-section with favourable bendingproperties;

an accompanying forming into a bendable cross-section during the bendingprocess;

a shaping of bendable cross-sections in extrusion profiles, preferablyfrom an aluminium alloy, without the preceding or accompanying formingprocess.

The inventor forces targeted folds during bending or he compresses thematerial flat; if necessary he shapes extrusion profiles in the startingcondition correspondingly as flat upright profiles in order thus toachieve a small moment of surface inertia so that corresponding slightplastic distortions are produced in the bending forming process. Only inthe ensuing IHPF process will the workpiece be shaped to its final form.

In the combination of bending and IHPF process in accordance with thisinvention there is a distinct separation of tasks:

the bending process is used to shape the component centre line,

the IHPF process is used to form the cross-section.

In this procedure above all a minimisation of the degree of forming isachieved rather than a simplification of technical complexity withregard to bending. In the bending process in accordance with thisinvention, the achieved degree of forming is diminished substantiallycompared to a bending process after a procedure taken from the state ofthe art. With a classic bending technology in which the aim of thebending process is to achieve a cross-sectional contour as close aspossible to the desired end result, only in exceptional cases arefavourable results achieved in relation to the accumulated plasticdistortions. In contrast, in the use of the bending strategy inaccordance with this invention, due to the lower forming degree in theensuing IHPF process, a higher residual forming capacity is available.

The bending procedure in accordance with this invention for themanufacture of IHPF components offers substantial advantages, including:

Greater shaping can be achieved in the IHPF process with the samematerial, i.e. there is more freedom in the shape of the end contour ofa IHPF component; and

IHPF components with far smaller radii of curvature are possible withthe same cross-sectional dimensions.

Additional advantages, features and details of the invention can befound in the following description of the preferred embodiment examplesand from the drawing; this shows in:

FIG. 1: an oblique view of a curved square profile;

FIGS. 2, 3, 4: three sketches of the steps of a bending procedure;

FIG. 5: an enlarged oblique view of the product of the bendingprocedure;

FIG. 6, 7: sketches pertaining to a calculating procedure;

FIG. 8, 9, 10: each a cross-section through an initial profile for themanufacture of the square profile;

FIG. 11: an oblique view of an initial profile with the cross-section inFIG. 10; and

FIGS. 12 to 15: four sketches pertaining to the course of the shaping ofhe square profile.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

From the square pipe 10 with a width b of 80 mm and a cross-sectionalheight h of 50 mm, during a bending procedure with an ensuing IHPFprocess an angle peice 11 is manufactured containing pipe sections 11_(q), 11 _(t) running at right angles to each other with an internalcurvature radius R_(i) of 200 mm.

FIGS. 2 to 5 show the bending of a pipe profile 10_(a) of roundcross-section to an angle piece 11_(a) with a curvature angle q of 90°;in the course of this procedure each pipe profile 10 _(a) is positionedbetween two roll-like tools 12, 12 _(r) in such a way that here it liestangentially on one of the tools 12 of this tool pair approximatelyoutside its linear centre, after which the other tool 12 _(r) is movedin translation in direction x up to the pipe profile 10 _(a) as acounter-tool. The movable tool 12 _(r) then makes its way around thestationary tool 12 in a rotational direction y and thereby takes with itthe upper pipe section 11 _(q) in FIGS. 2 to 4 with the pipe profile 10_(a) from the longitudinal axis A.

The view in FIG. 5 shows that said pipe profile 10 _(a) has beenindented on the stationary tool 12 in the support area during thebending procedure. This distorted area G determines intervals e, e₁ withthe end contours 13 of the pipe profile 10 _(a) and the angle pieces 11_(a). Its vertical centre line is indicated by M.

The following theoretical considerations form the basis of themanufacturing procedure, with reference to FIGS. 6, 7. A profile section14 has in its starting condition according to FIG. 6 the local curvatureradius R_(mA) and is bent into its end condition 14 _(a) according toFIG. 3 in such a way that the curvature radius R_(mB) arises in this endcondition; the two curvature radii R_(mA) and R_(mB) each refer to thebend-neutral fibres of the cross-section. On the assumption that noalteration to the cross-section occurs during bending, for extension zat any point at a distance z from any neutral fibre w have:$ɛ_{z} = {\frac{l_{zB} - l_{zA}}{l_{zA}} = \frac{{W_{2}\left( {R_{mB} + Z} \right)} - {W_{1}\left( {R_{m\quad A} + Z} \right)}}{W_{1}\left( {R_{m\quad A} + Z} \right)}}$

where l_(zA), l_(zB) are the lengths before and after the bendingprocess, W₁ the angle enclosed by the pipe and profile section 14 beforebending and W₂ the angle enclose by the profile section 14_(a) afterbending.

The length of the neutral fibre remains constant on bending withoutsuper-imposed stretching:

W ₂ R _(MB) =W ₁ R _(mA)

After the implementation and forming process the result is$ɛ_{z} = {{\frac{Z\left( {R_{m\quad A} - R_{mB}} \right)}{R_{m\quad A}\left( {R_{m\quad A} + Z} \right)}\quad {or}\quad ɛ_{z}} = \frac{Z\left( {1 - {R_{mB}/R_{m\quad A}}} \right)}{R_{mB}\left( {1 + {Z/R_{m\quad A}}} \right)}}$

for elongation at any point at a distance z from the neutral fibre. Forthe exception of a non-curved starting material (R_(ma)=∞) the result is$ɛ_{z} = \frac{Z}{R_{mB}}$

Extreme values of elongation ε_(z) are produced for extreme distances zto the neutral fibre. In the event of symmetrical cross-sections with awidth b, z_(max)=b/2 and therefore$ɛ_{z} = {{\frac{b\left( {R_{m\quad A} - R_{mB}} \right)}{R_{mB}\left( {{2R_{m\quad A}} + b} \right)}\quad {or}\quad ɛ_{z}} = \frac{b\left( {1 - {R_{{mB}/}R_{m\quad A}}} \right)}{R_{mB}\left( {2 + {b/R_{m\quad A}}} \right)}}$

Under the given conditions, with equations (1) to (3) the elongationsoccurring in a pipe or profile 14, including the maximum elongationduring a bending formation can be estimated.

For example, in FIG. 8, a cross-sectionally cylindrical pipe profile 15with a diameter d of 80 mm and a wall thickness t of 2 mm should be bentbefore an IHPF process in such a way that an inner curvature radiusR_(i) of 200 mm is produced. In a conventional bending process, themaximum elongation at the outer radius can be estimated according to thesaid equation (3). With the given starting values

B=d=80 mm; R _(mA) =∞; R _(mB) =d/2+200 mm=240 mm

the following value is obtained

ε_(max)=16.7%

In order to reduce the maximum elongation occurring in the bendingprocess, the pipe cross-section is distorted before the bending processin such a way that an approximately elliptical cross-section is producedwith a height i of 112 mm and a width n of 48 mm with the main axesindicated by M and Q. The cross-sectional periphery of the ellipticalprofile 15 a, here 251.30 mm, remains the same as that of the circularpipe or pipe profile 15.

At the apex of the elliptical cross-section there is a curvature or apexradius r of 10 mm and as stated a total width n after the describeddistorted indentation of just 48 mm.

This indentation of the pipe profile 15 yields a maximum strain in theapex of the cross-section. Here too, the resulting maximum elongationscan be estimated by means of the said equation (3);

b=t=2 mm; R _(mA) =d/2=40 mm; R _(mB) =r=10 mm

giving a maximum circumference elongation of ε_(max)=7.3% as a result ofthat indentation of the pipe profile or pipe 15 at the apex point of theresulting profile 15 _(a) of elliptical cross-section.

Due to the reduced width of n=48 mm, the expansion on the outer radiusin the longitudinal direction in the ensuing bending process onlyamounts to ε_(max)=10.0%. With a bending process in which the pipecross-section has been previously distorted by indentation, the maximumelongation can be reduced by almost half in relation to conventionalbending techniques.

As the use of a circular cross-section in the bending process leads to acomparatively high degree of forming, it is better to choose anelliptical cross-section in this instance but this is unfavourable forthe feeding of a IHPF tool 30 as indicated in FIGS. 12 to 15; namelythis tool 30 cannot then be closed without crushing the previously bentworkpiece or profile 14 a.

On bending an optimal initial profile 16, resembling an “H” incross-section in accordance with FIG. 10, the same forming degree isachieved as with the elliptical cross-section. In addition, however, thebent workpiece can be inserted into the IHPF tool 30 without anyproblems.

The posed or folded initial profile 16 with a height i₁ of 50 mm and awidth n₁ of 48 mm is as stated of H-shaped cross-section with twoapproximately parallel vertical chambers 18, the outer supporting walls20 of which are bent inwards to the horizontal main axis Q. The innerchamber walls 22 are sections of bead-like recesses 24 of the base wall26 and the ridge wall 28 of the initial profile 16. The spacing s of thebottom of both recesses 24 corresponds roughly to one-sixth of theprofile height i₁.

Both the width n₁ of this initial profile 16 in oblique view as detailedin FIG. 11 and its cross-sectional periphery correspond to thecorresponding measurements of the elliptical profile 14 _(a) in FIG. 9.

The initial profile 16 produced during extrusion is placed in the tool32 comprising a base tool or holder part 30 and the top tool or coverpart 36. From these only those contours of the surface of the base tool32 that are relevant for the forming process are sketched with basewalls 33 and side walls 34 as well as the cover part 36.

FIG. 13 shows steps to extend the initial profile 16 by way of apressure medium introduced in its internal area 19. During this pressureprocess the base wall 33 and the side walls 34 of the base tool 32 andthe cover tool 36 are positioned on the inside of the initial profile 16lying in the tool area 38. The expansion of the base wall 26 and theridge wall 28 is thus very slight; the initial profile 16 folds due tothe pressure medium introduced into its internal area 19, almost to aconcertina-like shape, and thus fills out the tool area 38. Only towardsthe end of the folding process are the walls 20, 26, 28 of the profile16 expanded when the tool area 38 is distorted.

The square pipe 10 or angle piece 11 produced in tool 30 as describedabove is then taken out of the tool area 38 (FIG. 15).

What is claimed is:
 1. A process for forming and deforming a startingprofile of a component with a profile cavity into a curved end profile,comprising the following steps: manufacturing a metallic startingprofile with favorable bending properties in an extrusion process;bending the starting profile into a curved shape; and forming a contourof the end profile by internal high pressure produced in a sealedprofile cavity by way of a fluid active means, whereby during thebending step a center line of the component is molded and by applyingthe internal high pressure a cross-section of the component is distortedinto its end shape.
 2. A process according to claim 1, wherein themanufacturing step includes forming the starting profile to have asubstantially H-shaped cross-section with at least two roughly parallelchambers which are connected to each other.
 3. A process according toclaim 2, wherein the starting profile is formed to have supporting wallswhich are bent inwards cross-sectionally.
 4. A process according toclaim 2, wherein the starting profile is formed so that the chamber hasinner borders formed by groove-like recesses on base and ridge surfaceareas.
 5. A process for forming and deforming a starting profile of acomponent with a profile cavity into a curved end profile, comprisingfollowing steps: manufacturing a starting profile from a metal sheetwith favorable bending properties by bending and joining the metalsheet; bending the starting profile into a curved shape; and forming acontour of the end profile by internal high pressure produced in asealed profile cavity by way of a fluid active means, whereby during thebending step a center line of the component is molded and by applyingthe internal high pressure a cross-section of the component is distortedinto its end shape.
 6. A process according to claim 5, wherein themanufacturing step includes forming the starting profile to have asubstantially H-shaped cross-section with at least two roughly parallelchambers which are connected to each other.
 7. A process according toclaim 6, wherein the starting profile is formed to have supporting wallswhich are bent inwards cross-sectionally.
 8. A process according toclaim 6, wherein the starting profile is formed so that the chamber hasinner borders formed by groove-like recesses on base and ridge surfaceareas.
 9. A process for forming and deforming a starting profile of acomponent with a profile cavity into a curved end profile, comprisingfollowing steps: manufacturing a starting profile; mounting the startingprofile on a roll-like stationary tool and distorting the startingprofile cross-sectionally to get a cross-section with favorable bendingproperties while bending the starting profile by a translatory androtationally moveable, roll-like counter-tool into a curved shape; andforming a contour of the end profile by internal high pressure producedin a sealed profile cavity by way of a fluid active means, wherebyduring bending a center line of the component is molded and by applyinginternal high pressure the cross-section is distorted into its endshape.